European Patent Publication No. EP 0 937 004 A describes an apparatus for pneumatically pumping powdered materials having a receptacle which is connected to a supply pipe as well as a discharge for the pumped material and which is separated by at least one plate-like filter element from a chamber connected to a vacuum pipe; the width of the filter element corresponds at the maximum to the diameter of the receptacle. For pumping a material having a specific gravity from 0.1 to 15.0 g/cm3 as well as with a particle size range between 0.1 and 300 μm as the pumped material, the ratio of the length of the pump chamber-forming receptacle for temporarily containing the pumped material to its inside diameter is between 0.5 and 10.0, and the plate-like filter element is provided between a vacuum pipe of a vacuum pump for drawing in the material to be pumped and the pump chamber. Adjoining the chamber connected to the vacuum pump is a pumping gas pipe of a pumping gas source, and both in the vacuum pipe and in the pumping gas pipe is arranged in each case an automatic shut-off member.
EP 0 538 711 A describes a pumping apparatus for example for plastics granulates having a hosepipe which at one end enters a storage silo by means of a lance and at the other end extends through a filter carrier into a pipe connection which is seated on the box-like inlet of a tangential feed opening of a plasticisation cylinder. Above the filter carrier is provided a cover assembly also traversed by the hosepipe and having a suction chamber. The latter has suction openings directed towards the pipe connection and is operatively connected to a nozzle system to which compressed air or compressed gas can be delivered as the working medium. In the suction chamber is generated a relatively high partial pressure which is propagated through the suction openings and the filters into the pipe connection and from there through the hosepipe into the storage silo. This working medium is intended to generate such a high pressure, due to the increase in its speed in the material being pumped, that the solids are drawn to the box-like inlet, while mixing with a suction air stream. At the filters, the solids are separated from the suction air stream and the latter is mixed with the working medium. Filter cleaning cannot be carried out during the process.
According to the state of the art, pumping apparatuses of this kind are tailored to a certain product, that is, to the pumping of powders or the pumping of liquid. Of course some diaphragm pumps may pump powder and liquids, but inefficient treatment of powder is possible only to a minor extent, and only when the powder substance is particularly adapted to the process.
The pumping of suspensions is difficult insofar as the powder in a suspension tends to be deposited in the pipes or closure valves, leading to blockage of the pumping system.
The present invention is directed to an apparatus and a method of the kind mentioned hereinbefore which allow not only the pumping of such different products as liquids, powders and even suspensions or pastes with the same equipment, but also volumetric proportioning thereof.